Charlie McMurray is an intern at RSPB Scotland working on 'all nature' projects: mammals, amphibians and insects - basically everything that isn't birds! Charlie started at the RSPB in January and will be with us for nine months. So far the focus has been natterjack toads and this is an update on that work to this point. Stay tuned, we'll have plenty of updates for you.
Nattering about natterjacks
The New Year brought in a change of scenery for me. In early January, I set up sticks in Edinburgh to start my nine month internship with RSPB Scotland. As an undergraduate zoology student at Manchester, this is my opportunity to see behind the scenes and get stuck into various wildlife projects. So far, about 98% of my time has been taken up by the highly charismatic species, the natterjack toad. And, before the toads emerge after their winter slumbers, I’ve been getting to grips with the story so far...
In 1999, a small amount of natterjack spawn was translocated down the road from Southerness to Mersehead in Dumfries and Galloway. Increasing pressures on the toad’s habitat at Southerness (including an expanding caravan site) meant that the creation of a second population at Mersehead was seen as a sensible insurance policy to safeguard the future of the species in the area. However, in 2014 there was severe local saltwater flooding which raised concerns about the survival of these natterjacks. In response, a three-year survey was launched to see how (and if) they had coped.
So far, the news looks good for these robust amphibians. In 2014, about 45 toads were counted while in 2015, around 180 made themselves known. To get a more accurate estimate of the population size, we embarked on a mission to identify each and every toad at the site, which would help us to see if we were coming across the same individuals more than once.
To do this we needed a reliable way to tell the toads apart. Rather than marking each one invasively by clipping their toes, we decided to use the toad’s natural identifiers: their wart patterns. The beautiful thing about natterjacks is that they each come with their own ID badge in the form of the big warts and the yellow stripe on their backs. Each pattern is completely unique and remains the same throughout its owner's lifetime, just like a human fingerprint. During the 2014 and 2015 seasons, the natterjack team took ‘mugshots’ of as many toads as possible to build up a database.
As that database has grown, it’s become increasingly difficult to identify individual toads by eye alone. It’s taken a whole week to work through our ‘mugshots’ (and there are more to go!).
See if you can have a go yourself...
To ease and quicken the process, we’ve been looking into using recognition programmes, most notably I3S. I3S aids individual recognition of different animals, making it semi-manual rather than fully manual. It’s been used to identify whale flukes, patterns on salamanders and whale sharks, and markings on manta rays. Other studies have shown this to be a really useful aid in surveys like ours, so there was every reason to be hopeful.
Creating the wart pattern database on I3S: the user defines three reference points (tail base and both armpits) and pick out each wart.
A visual representation of an I3S comparison of two wart patterns (red and blue). The green lines show good wart matches. These patterns match (verified by eye) with a low score of 10.62.
The user manually picks out the wart pattern and this is saved within the database. I3S then compares it to the other saved patterns and gives a list of the possible matches or ‘suspects’ along with a score. The lower the score is, the better the match, but each is verified by eye.
Disappointingly, the results from I3S haven’t been as promising as we’d hoped for so far. Between 2014 and 2015, it found only four recaptured individuals, whereas I found nine using eye alone. That leaves the programme’s success rate at only 44% in this situation.
I’m now looking into why man outperformed machine so convincingly. Perhaps there are simple fixes though: we may just need to perfect our photography skills and be really strict about the toad’s posture. How many thoroughly independent and feisty toads do you think will be likely to pose willingly?
I have yet to compare individuals for 2015. Hopefully, a solution will have presented itself before I subject myself to hours of spot-the-difference accompanied by countless podcasts. If not, I guess I’ll be feeling warty-eyed for the next few months.
Despite the bumps in the road for quick and easy identification, there is every reason to be optimistic about how the toads are faring. The recapture rate is low, suggesting that the population might be bigger than we’d predicted and proving that natterjacks really are made of tough stuff.
Hopefully, they’re snug in their burrows at the moment, pondering over how to give us some more fantastic data this year. Let’s keep our fingers crossed for a strong season – we’ll keep you up to date!